docs: def get_bmus(self, activation_map):
          """Returns Best Matching Units indexes of the activation map.
  
          :param activation_map: Activation map computed with self.get_surface_state()
          :type activation_map: 2D numpy.array
  
          :returns: The bmus indexes corresponding to this activation map
                    (same as self.bmus for the training samples).
          :rtype: 2D numpy.array
          """
  
          Y, X = np.unravel_index(activation_map.argmin(axis=1),
                                  (self._n_rows, self._n_columns))
          return np.vstack((X, Y)).T